3/31/2023 0 Comments Chrome js blocker![]() ![]() ![]() JavaScript is a popular scripting language that's used to make web pages interactive. Improve first page load performance: render JavaScript templates on the server to deliverįast first render, and then use client-side templating once the page is loaded.Why do I need JavaScript enabled on Google Chrome? Similarly, leveraging server-side rendering can significantly Then you should investigate inlining the relevant JavaScript modules to avoid extra ![]() What if I'm using a JavaScript framework to construct the page? If the content of the page is constructed by client-side JavaScript, Investigate making such JavaScript asynchronous or defer its loading. However, many of theseīehaviors can be safely added after the above-the-fold content is rendered. Doing so can help reduce resource contention and improve performance.įAQ What if I am using a JavaScript library such as jQuery? Many JavaScript libraries, such as JQuery, are used to enhance the page to addĪdditional interactivity, animations, and other effects. The loading and execution of scripts that are not necessary for the initial page render may beĭeferred until after the initial render or other critical parts of the page have finished The DOM or CSSOM of the page may need to be rewritten to account for these constraints. Scripts that depend on execution order or need to access or modify Note that asynchronous scripts are not guaranteed to execute in specified order and should not useĭocument.write. Asynchronous JavaScript to learn more about asynchronous scripts. Prevent JavaScript from blocking the parser we recommend using the HTML asyncĪttribute on external scripts. As a result, you should only inline small scripts to deliver best performance.īy default JavaScript blocks DOM construction and thus delays the time to first render. The size of the HTML document and that the same script contents may need to be inlined across However, note that inlining also increases The browser to deliver a faster time to first render. Inlining the script contents eliminates the external request for small.js and allows Then you can inline the script as follows: * contents of a small JavaScript file */ For example, if the HTML document looks like this: Scripts are small, you can inline their contents directly into the HTML document and avoid the Which may add one or more network roundtrips before the page can be rendered. That for this to improve your loading time, you must alsoĮxternal blocking scripts force the browser to wait for the JavaScript to be fetched, Render should be made asynchronous or deferred until after the first render. Scripts that are necessary to render page contentĬan be inlined to avoid extra network requests, however the inlined content needs to be smallĪnd must execute quickly to deliver good performance. Must be fetched before they can be executed. ![]() You should avoid and minimize the use of blocking JavaScript, especially external scripts that In the case of an external script the parser is alsoįorced to wait for the resource to download, which may incur one or more network roundtrips andĭelay the time to first render of the page.Īdding Interactivity with JavaScript to learn more about how JavaScript affects the critical This rule triggers when PageSpeed Insights detects that your HTML references a blockingĮxternal JavaScript file in the above-the-fold portion of your page.īefore the browser can render a page it has to build the DOM tree by parsing the HTML markup.ĭuring this process, whenever the parser encounters a script it has to stop and execute itīefore it can continue parsing the HTML. Version 5 is the latest and providesīoth real-world data from the Chrome User Experience Report and lab data from Lighthouse. This page was written for version 4 of the PageSpeed Insights API, which isĭeprecated and will be shut down in May 2019. ![]()
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